Congratulations on the interview invite! This really comes down to comfort but I'll lay out the pros and cons for both followed by my suggestion.
Pros: you keep the rapport and build upon - the comfort level is high in this option
Cons: you limit the perspectives into your application. If they are debating your profile versus someone equally qualified, the other applicant may have 2 or 3 people speaking on their behalf versus your one.
Pros: The opposite of the con above. Additionally, it gives you the opportunity to answer questions in a slightly different way so that you can cover more key themes in your application that they can take back to the decision committee.
Conts: Definitely a little more risk. You don't know this person - you might not get along with them at all!
My suggestion - go with someone new. Not only do you get to cover more bases but if you developed a great rapport with the other adcom person, you should be ok here too.
Good luck and if you have any interview specific questions, please let me know!
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